effect-io-ai

Package: effect
Module: Data

Data.TaggedEnum

Transforms a record of variant definitions into a discriminated union type.

When to use

Use when you have two or more variants that share a common _tag discriminator.

Details

Each key in the record becomes a variant with readonly _tag set to that key. Use with taggedEnum to get constructors and matchers.

Gotchas

Variant records must not include a _tag property; it is added automatically.

Example (Defining a tagged enum)

import { Data } from "effect"

type HttpError = Data.TaggedEnum<{
  BadRequest: { readonly status: 400; readonly message: string }
  NotFound: { readonly status: 404 }
}>

// Equivalent to:
// | { readonly _tag: "BadRequest"; readonly status: 400; readonly message: string }
// | { readonly _tag: "NotFound"; readonly status: 404 }

const { BadRequest, NotFound } = Data.taggedEnum<HttpError>()

const err = BadRequest({ status: 400, message: "missing id" })
console.log(err._tag)
// "BadRequest"

See

• taggedEnum — constructors and matchers for a TaggedEnum
• TaggedEnum.WithGenerics — generic tagged enums
• TaggedEnum.Constructor — the constructor object type

Signature

type TaggedEnum<A> = keyof A extends infer Tag ? Tag extends keyof A ? Types.Simplify<
      { readonly _tag: Tag } & { readonly [K in keyof A[Tag]]: A[Tag][K] }
    >
  : never
  : never

Source

Since v2.0.0